In recent years in the fields of wireless LAN and PLC (Power Line Communication), instead of a mode in which the whole communication system is managed by a single base station, an ad-hoc network that expands its communication range in association with a size-increase of the communication system by allowing each terminal included in the system to conduct a relay for other terminals is adopted.
With the ad-hoc network, it is necessary to create a communication route indicating through which terminals a communication packet is relayed, for a transmission of the communication packet to a desired final destination. A proactive protocol (e.g., refer to Non Patent Literature 1, 2) and a reactive protocol (e.g., refer to Non Patent Literature 3, 4) are existing protocols for creating the communication route.
In the proactive protocol, each of the terminals in the system periodically transmits a route creation packet to each other through broadcast. Each of the terminals in the system writes information of a destination of its own terminal in the route creation packet received from other terminals, and transfers the packet to other terminals. Then, each of the terminals in the system creates a route, based on information of the destinations of the multiple terminals, which is included in the received route creation packet. An advantage of the proactive protocol is that a load at the time of a transmission of the communication packet is small, since a route creation is conducted beforehand independently of the transmission of the communication packet. On the other hand, a disadvantage of the proactive protocol is that a load on the whole system is large because of the amount of the route creation packets occupying a communication network is large, since the route creation packet is transmitted regardless of presence or absence of the transmission of the communication packet.
In the reactive protocol, when conducting a communication, a terminal in the system confirms a route to a desired final destination by transmitting a route creation packet through broadcast only prior to the communication. An advantage of the reactive protocol is that a load on the whole system is small, because the route creation packet is transmitted only when necessary, resulting in a small amount of route creation packets occupying the communication network. On the other hand, an advantage is that a load at the time of the transmission of the communication packet is large, since it is necessary to always conduct a route creation prior to the transmission of the communication packet.
As a result of taking into consideration of the advantages and the disadvantages of the proactive protocol and the reactive protocol described above, there is a general tendency to adopt the proactive protocol for a communication system with frequent communications, and to adopt the reactive protocol for a communication system with infrequent communications.